is there really something that does that? I have heard that but always figured it was an urban myth - if there is, I may get some!
What makes eyes burn? Smells like "chlorine? "
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No, but if chem-geek can come up with something, he'll be rich. And I think we deserve a cut, don't you?
heck, I don't need a cut - I would be happy to pay his royalty if I could get some of it!
thanks for the replies so far - thanks for your patience as I continue to ask dumb questions
So the pool is always getting various organic materials in it that are bad - sweat, pee, rotting leaves, etc. And we maintain free chlorine in the water so that these things will get "eaten." The FC turns to CC when it reacts with these different contaminants. So far so good?
We also put CYA in the water so that the sunlight does not break down the FC as quickly. But that also means we need to keep more FC in the water since some of it will be rendered ineffective by the CYA. Still good?
So why doesn't the CC level in the pool continue to go up and up as the FC is turned to CC and we add more and more FC every day to get rid of the organics? I think I understand that some of the CC (as well as some of the FC) is broken down by UV from sunlight. So in most cases, does the sun break down the CC as fast as it is produced? If so, then if we see higher CC levels, does that mean the rate of organic addition to the water results in CC being produced faster than it can be broken down by the sun? And is urine a particularly bad situation because it generates a big chlorine demand? Or because it makes a particular type of CC that takes a long time to break down? Is CC also broken down by FC? Do we super chlorinate to get rid of CC? If so, is it because CC needs a breakpoint FC level to break it down? Or is that just true of certain kinds of CC?
In a nutshell, I would like to better understand the underlying chemistry so I can better understand how to control CC.
Again, thanks for the patience and continued responses.
So the pool is always getting various organic materials in it that are bad - sweat, pee, rotting leaves, etc. And we maintain free chlorine in the water so that these things will get "eaten." The FC turns to CC when it reacts with these different contaminants. So far so good?
We also put CYA in the water so that the sunlight does not break down the FC as quickly. But that also means we need to keep more FC in the water since some of it will be rendered ineffective by the CYA. Still good?
So why doesn't the CC level in the pool continue to go up and up as the FC is turned to CC and we add more and more FC every day to get rid of the organics? I think I understand that some of the CC (as well as some of the FC) is broken down by UV from sunlight. So in most cases, does the sun break down the CC as fast as it is produced? If so, then if we see higher CC levels, does that mean the rate of organic addition to the water results in CC being produced faster than it can be broken down by the sun? And is urine a particularly bad situation because it generates a big chlorine demand? Or because it makes a particular type of CC that takes a long time to break down? Is CC also broken down by FC? Do we super chlorinate to get rid of CC? If so, is it because CC needs a breakpoint FC level to break it down? Or is that just true of certain kinds of CC?
In a nutshell, I would like to better understand the underlying chemistry so I can better understand how to control CC.
Again, thanks for the patience and continued responses.
The reason the CC doesn't continue to climb is that more chlorine oxidizes the CC creating end products that are no longer CC. In the case of ammonia, chlorine reacts quickly with it to form monochloramine which is CC, but then it further reacts with it more slowly to form dichloramine (still a CC) which reacts with the monochloramine to form nitrogen gas and hydrochloric acid neither of which are CC. So there is no longer any CC since the chlorine is no longer bound to the nitrogen and instead got reduced to chloride salt.
And as I wrote and you understood, some CC is broken down by sunlight either directly or indirectly and here again the chlorine that was bound to ammonia or the organic gets converted (eventually) to chloride salt. So the "buildup" from chlorine usage/consumption is chloride salt (technically sodium chloride salt because of the sodium from chlorinating liquid or bleach that balances the chlorine in hypochlorite). The oxygen from the hypochlorite ends up as either water (for oxidation of ammonia and organics) or as oxygen gas (when chlorine breaks down from sunlight). Technical details are in this post.
And yes, when you see CC buildup in your pool it most likely means that you are introducing ammonia and organics (ones that can combine with chlorine) faster than the sum of sunlight breaking it down or chlorine further oxidizing it is able to keep up. Assuming you are maintaining proper chlorine levels, the easiest way to fix this is to expose the pool to sunlight longer. For an indoor pool or any pool not exposed to sunlight one can add a UV system.
Urine is indeed particularly bad because it contains a lot of nitrogenous components that can react with chlorine, especially urea, ammonia, and creatinine, but also amino acids (see this post for more details). One cup of urine is equivalent to 5 person-hours of bather load. Urine is also worse than sweat because it contains a higher content of urea and urea reacts rather slowly with chlorine so builds up unless sunlight is present (we think because sunlight breaking down chlorine creates hydroxyl radicals that oxidize the urea before it gets a chance to react with chlorine).
Superchlorination (i.e. raising the FC/CYA ratio) will help get rid of CC for CC that is ammonia based (i.e. inorganic chloramines), but can make the problem worse creating more CCs for slow-to-oxidize organics such as urea especially if it has built up in the pool. If the introduction of urea is stopped, then superchlorination can eventually get rid of the urea and the CCs but this can be slow. Some commercial/public pools try and do this by superchlorinating at night but this is not always successful due to the high bather-loads during the day.
There is no such thing as breakpoint for a pool because you are always maintaining chlorine in the pool. The term "breakpoint" comes from adding chlorine to ammonia in terms of how much chlorine is needed to get over the hump to oxidize it. However, that is not the situation in the pool because you are always adding chlorine to maintain its level and the much smaller amount of ammonia is only slowly getting introduced so "breakpoint" is continuous. The concentration of active chlorine (proportional to the FC/CYA ratio) determines how quickly the chemical reactions with chlorine occur, but there isn't some magic concentration where all of a sudden things start to happen. It's continuous where higher chlorine levels make the reactions go faster. The reaction rate is determined by the concentration (so proportional to the FC/CYA ratio) but the stoichiometric quantity of chlorine that is required gets taken from the chlorine reserve (i.e. the FC which is mostly chlorine bound to CYA) and is replenished when you add more chlorine.
However, there is a downside for using chlorine to oxidize bather waste because for some of the reactions higher chlorine levels can produce more nitrogen trichloride that is the most volatile and irritating chloramine. In fact, there is a substantial amount of nitrogen trichloride produced from the chlorine oxidation of urea which is why sunlight is important to get rid of the urea rather than have chlorine try and oxidize it. See this post for more technical details.
And as I wrote and you understood, some CC is broken down by sunlight either directly or indirectly and here again the chlorine that was bound to ammonia or the organic gets converted (eventually) to chloride salt. So the "buildup" from chlorine usage/consumption is chloride salt (technically sodium chloride salt because of the sodium from chlorinating liquid or bleach that balances the chlorine in hypochlorite). The oxygen from the hypochlorite ends up as either water (for oxidation of ammonia and organics) or as oxygen gas (when chlorine breaks down from sunlight). Technical details are in this post.
And yes, when you see CC buildup in your pool it most likely means that you are introducing ammonia and organics (ones that can combine with chlorine) faster than the sum of sunlight breaking it down or chlorine further oxidizing it is able to keep up. Assuming you are maintaining proper chlorine levels, the easiest way to fix this is to expose the pool to sunlight longer. For an indoor pool or any pool not exposed to sunlight one can add a UV system.
Urine is indeed particularly bad because it contains a lot of nitrogenous components that can react with chlorine, especially urea, ammonia, and creatinine, but also amino acids (see this post for more details). One cup of urine is equivalent to 5 person-hours of bather load. Urine is also worse than sweat because it contains a higher content of urea and urea reacts rather slowly with chlorine so builds up unless sunlight is present (we think because sunlight breaking down chlorine creates hydroxyl radicals that oxidize the urea before it gets a chance to react with chlorine).
Superchlorination (i.e. raising the FC/CYA ratio) will help get rid of CC for CC that is ammonia based (i.e. inorganic chloramines), but can make the problem worse creating more CCs for slow-to-oxidize organics such as urea especially if it has built up in the pool. If the introduction of urea is stopped, then superchlorination can eventually get rid of the urea and the CCs but this can be slow. Some commercial/public pools try and do this by superchlorinating at night but this is not always successful due to the high bather-loads during the day.
There is no such thing as breakpoint for a pool because you are always maintaining chlorine in the pool. The term "breakpoint" comes from adding chlorine to ammonia in terms of how much chlorine is needed to get over the hump to oxidize it. However, that is not the situation in the pool because you are always adding chlorine to maintain its level and the much smaller amount of ammonia is only slowly getting introduced so "breakpoint" is continuous. The concentration of active chlorine (proportional to the FC/CYA ratio) determines how quickly the chemical reactions with chlorine occur, but there isn't some magic concentration where all of a sudden things start to happen. It's continuous where higher chlorine levels make the reactions go faster. The reaction rate is determined by the concentration (so proportional to the FC/CYA ratio) but the stoichiometric quantity of chlorine that is required gets taken from the chlorine reserve (i.e. the FC which is mostly chlorine bound to CYA) and is replenished when you add more chlorine.
However, there is a downside for using chlorine to oxidize bather waste because for some of the reactions higher chlorine levels can produce more nitrogen trichloride that is the most volatile and irritating chloramine. In fact, there is a substantial amount of nitrogen trichloride produced from the chlorine oxidation of urea which is why sunlight is important to get rid of the urea rather than have chlorine try and oxidize it. See this post for more technical details.
wow - that is an outstanding explanation in easy to understand language - thanks chemgeek
so, if I understand...
FC reacts with organics to make CC - the CC continues to react with FC until it is no longer CC - sunlight also gets rid of CC
under normal load, reasonable FC addition and sunlight will keep up with the reaction of organics to form CC and further reaction to eliminate CC
under particularly heavy load, FC can still keep up, but it may have to be kept high which may lead to the formation of particularly irritating chloramines
there is no magic FC level - it is all about concentration vs rate, so heavy load requires high levels to drive the reactions fast enough to keep up
urine is particularly bad because it makes for a heavy load for the FC to bear, and the urea in particular is slow to react with FC without sunlight
so, to keep my pool nice and avoid eye irritation from CC (vs pH), the key is to maintain proper FC and pH, be sure my rate of FC addition is maintaining the proper FC level considering CYA level, ensure nobody is peeing in the pool and give the pool some "sun time" to help with the CC elimination
and if I ever have an unusual heavy load, and the FC drops way low (below minimum for the CYA level) and I see any CC (or at least anything over 0.5), I should SLAM the pool right away
is that correct?
so, if I understand...
FC reacts with organics to make CC - the CC continues to react with FC until it is no longer CC - sunlight also gets rid of CC
under normal load, reasonable FC addition and sunlight will keep up with the reaction of organics to form CC and further reaction to eliminate CC
under particularly heavy load, FC can still keep up, but it may have to be kept high which may lead to the formation of particularly irritating chloramines
there is no magic FC level - it is all about concentration vs rate, so heavy load requires high levels to drive the reactions fast enough to keep up
urine is particularly bad because it makes for a heavy load for the FC to bear, and the urea in particular is slow to react with FC without sunlight
so, to keep my pool nice and avoid eye irritation from CC (vs pH), the key is to maintain proper FC and pH, be sure my rate of FC addition is maintaining the proper FC level considering CYA level, ensure nobody is peeing in the pool and give the pool some "sun time" to help with the CC elimination
and if I ever have an unusual heavy load, and the FC drops way low (below minimum for the CYA level) and I see any CC (or at least anything over 0.5), I should SLAM the pool right away
is that correct?
I've learned a lot by reading this thread. Thanks for your good questions and for chemgeeks answers.
Now that I know so much, I cringe at how often I probably had nAsty water in my pool. I have started adding - half gallon of bleach or a gallon any time we have lots of swimmers. It just makes me feel better. I have an SWG and love it, but Bleach is a quicker chlorine add to accommodate the loss from lots of swimmers.
[emoji176] Lisa P.
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Now that I know so much, I cringe at how often I probably had nAsty water in my pool. I have started adding - half gallon of bleach or a gallon any time we have lots of swimmers. It just makes me feel better. I have an SWG and love it, but Bleach is a quicker chlorine add to accommodate the loss from lots of swimmers.
[emoji176] Lisa P.
Sent from my iPhone using Tapatalk
You got it except for the last point where it isn't always necessary to SLAM the pool just because the chlorine got low and you see CC. You may be able to just get back to a normal chlorine level or perhaps a higher than normal but below SLAM level and do fine. The SLAM level is more for killing off clumped algae. You can SLAM if you want to and reactions should go faster, but it may not be necessary. Generally you want to just get to the proper FC/CYA level and expose the pool to more sunlight. Usually that's enough.
If you know ahead of time that you will be having higher bather load, you can elevate the chlorine level in anticipation, though not too much since you don't want it to be unpleasant for the bathers (and by "unpleasant" I mean someone may notice the chlorine in the pool -- it's not really unpleasant).
To give you some perspective on the rate of different chemical reactions, with typical FC/CYA levels in our pools chlorine combines with ammonia to form monochloramine very quickly in about one minute. Chlorine is then much slower to combine with monochloramine to form dichloramine but when it does the monochloramine and dichloramine combine to form nitrogen gas quickly. So this latter two-step is mostly (90%) completed in about 4 hours. This assumes the ammonia is introduced all at once which of course is not how it works in pools, but this just gives you a rough idea.
If you know ahead of time that you will be having higher bather load, you can elevate the chlorine level in anticipation, though not too much since you don't want it to be unpleasant for the bathers (and by "unpleasant" I mean someone may notice the chlorine in the pool -- it's not really unpleasant).
To give you some perspective on the rate of different chemical reactions, with typical FC/CYA levels in our pools chlorine combines with ammonia to form monochloramine very quickly in about one minute. Chlorine is then much slower to combine with monochloramine to form dichloramine but when it does the monochloramine and dichloramine combine to form nitrogen gas quickly. So this latter two-step is mostly (90%) completed in about 4 hours. This assumes the ammonia is introduced all at once which of course is not how it works in pools, but this just gives you a rough idea.
chemgeek - thanks for the clarification - and I will definitely raise to close to shock levels before a really big load in the future
what is the signal that a SLAM is needed?
what is the signal that a SLAM is needed?
If you have high CC and cannot pass the overnight free chlorine loss test, then you need to SLAM. Have the directions to the OCLT been posted yet?
[emoji176] Lisa P.
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[emoji176] Lisa P.
Sent from my iPhone using Tapatalk
Lisa - thanks - I am familiar with that test - so if I see the FC drop "too low" and see some CC, do the OCLT, and if it is high, then SLAM, and if it is good, then no SLAM needed
The OCLT tells you that something is consuming chlorine in the pool at too high a rate. Most often that is an indicator of some algae growth even if it is not yet visible. A SLAM kills it off before it gets any further. The OCLT is a far better indication of something going wrong that needs a SLAM than having the CC be high. Algae growth does not usually show up as CC because any chlorine combining with algae tends to stay with the algae so unless it's free-floating everywhere including the water sample you take, you won't measure it.
Thanks chemgeek. That's good to know!! I'm still learning everyday!
[emoji176] Lisa P.
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[emoji176] Lisa P.
Sent from my iPhone using Tapatalk